Editor                                      

  To specify that an external editor is used when you press F4,
  press the space bar.

       +------------------- Edit -------------------+
       | Select which editor to use for F4:         |
       |   (.) Built-in                             |
       |   ( ) External                             |
       +--------------------------------------------+

 You can specify the editor you want to use when you press F4,
 by associating an editor to an extension. You can do this
 using the Editors... command from the Commands menu.